EP3832173B1 - Bellows, use of same and method for producing same - Google Patents

Description

technical field

The invention relates to a bellows, its use and a method for its production.

The bellows has an at least two-layer structure, comprising at least one first layer and at least one second layer, which are non-detachably connected to one another for production reasons, the layers having different densities.

State of the art

Bellows are well known and often consist of thermoplastic elastomers. The previously known bellows have a single-layer structure and are produced from a blown tube by extrusion blow molding, among other things.

Due to the single-layer structure, a bellows can often only be inadequately adapted to the respective circumstances of the application. Partial areas of a single-layer bellows also inevitably consist of the one material used, for which another material might be better suited, for example with regard to the usage properties, one if possible low weight or more economical manufacturability. In particular, when the material used is expensive, the bellows made from it also becomes expensive.

From the DE 102 49 073 A1 is a bellows, as described above, known. The previously known bellows is designed as a multi-layer bellows, with each layer having different material properties from one another, which makes it possible to use different materials that can be optimized individually, for example for the interior or exterior of a bellows. The inner area of the bellows can therefore be formed by a material that is particularly elastic and resistant to a lubricant that is used. On the other hand, a material that is particularly resistant to environmental influences such as UV light, aggressive media or moisture is used on the outside of the bellows. The multi-layer bladder includes a core layer and at least one skin layer, wherein the at least one skin layer is an outer layer of the multi-layer bladder. The multiple layers are considered advantageous in order to be able to optimize quality-determining factors, such as elasticity and surface properties, largely independently of one another. In addition, the low cost of the multi-layer bellows is emphasized. The previously known multi-layer bellows can have a core layer made of a foamed material in order to minimize the use of expensive materials. The foamed core layer is protected by the fact that the core layer is surrounded by skin layers and is thus protected from external influences. The sandwich-like multi-layer bellows is manufactured by a co-extrusion process.

From the DE 32 36 308 A1 an elastic bellows is known, with a layer structure having at least two layers, one layer consisting of a soft polyvinyl chloride and one layer consisting of at least one thermoplastic elastomer.

From the DE 10 2018 214 173 A1 a bellows for a steering system of a motor vehicle is known. The bellows is designed as a multi-layer bellows and includes at least two layers of different materials. Due to the different materials of the layers, a functional separation is achieved. The first type of material is mainly intended to create a barrier against moisture, vapour, gas, water (protection against corrosion) and the second type of material is mainly intended to absorb mechanical energy (impact energy of foreign objects) coming from the environment on the system and thus on the Material can act to absorb. One layer can consist of a thermoplastic elastomer, another layer of fiber-reinforced plastic, for example.

From the DE 80 01 872 U1 Another bellows is known, which is designed as a multi-layered bellows. The layers of the bellows are connected to each other by an adhesive bond.

From the US 6,386,551 B1 a multi-layer bellows is known, which is produced by a coextrusion process. The layers used consist of different materials.

Presentation of the invention

The invention is based on the object of further developing a bellows and a method for its production in such a way that the bellows has good recyclability, in particular is recyclable by type. In addition, the bellows should have good usage properties over a long period of use, be able to be better adapted to the particular circumstances of the application, and the bellows should be simple and inexpensive to produce.

A use of such a bellows should also be mentioned.

This object is achieved according to the invention by the features of claims 1, 9 and 10. The claims referring back directly or indirectly to claim 1 refer to advantageous configurations of the bellows.

To solve the problem, a bellows is provided with an at least two-layer structure, comprising at least one first layer and at least one second layer, which are permanently connected to one another for manufacturing reasons, the layers having different densities and the first layer and the second layer being made of the same material Material exist and wherein the material is unfoamed from one of the layers and foamed from one of the layers.

The advantage here is that the different layers of the bellows are each functionally individualized. For example, each material is only used for the layer for which it is also suitable/required in order to ensure good service properties of the bellows over a long service life. The use of a material that is oversized, for example in terms of price, weight and durability, is no longer necessary thanks to the multi-layer structure of the bellows. Every Layer can be formed as required for good performance over a long period of use, with particular consideration of economic manufacturability.

If one of the layers, as will be explained later, is made from a foam material, for example, material is saved compared to a layer made from a non-foamed material, so that the bellows can be produced more cheaply and easily overall.

Such a design means that the handling of the bellows according to the invention remains simple in comparison to a bellows with only a single-layer structure. In particular, the assembly and disassembly of the bellows, as well as the functional properties of the bellows during its intended use, do not differ from good single-layer bellows, if only advantageously.

The layers have different densities. With such a configuration, there are many possible variations, so that such a bellows with an at least two-layer structure can be adapted particularly well to the respective requirements of the application.

In order to be able to carry out the recycling of a bellows that is no longer required as simply as possible, it is provided that the layers consist of mutually compatible materials. This is also beneficial for good bonding of the layers.

Bellows whose layers are made of the same material are particularly easy to recycle. Sorted recycling is thereby possible. This is particularly useful when at least one of the layers consists of the same foamed material.

A material that is particularly well suited for the production of bellows in many cases is a TPE material. Bellows made of a TPE material have the advantage that, compared to conventional thermoplastics, they allow large deformations with low forces.

It is therefore preferably provided that the layers consist of a TPE material.

The first layer and the second layer are made of the same material, with the material of one of the layers being unfoamed and one of the layers being foamed.

For an unfoamed layer, with the same thickness, comparatively more material is required than for a foamed layer. For example, the unfoamed layer can form the outer layer of the bladder, while the foamed layer can form the inner layer or one of the inner layers. The relatively more sensitive foamed layer is replaced by the unfoamed and more resistant outer layer then effectively protected against external influences.

The material savings through a foamed layer compared to a non-foamed layer is usually around 30%, so that the bellows can be produced more cheaply, but despite the material savings it has the same required wall stability. This is achieved in that the necessary section modulus of a bellows wall with a solid-foamed-solid structure, for example, is achieved with only a slightly increased wall thickness equal to a solid layer.

The foamed layer can be physically or chemically foamed.

A physically foamed layer has the advantage that no blowing agent needs to be used, which in a way contaminates the plastic. Physical foaming takes place by injecting a gas, for example air or nitrogen, into the molten material during extrusion.

A chemically foamed layer has the advantage that there is no need for a gas injection unit on the production line.

Chemical foaming takes place by adding a blowing agent to the plastic.

In addition, an at least two-layer structure that includes a foamed layer has the technical advantage over a single-layer, non-foamed structure that such bellows have improved thermal insulation and are still recyclable if the foam is made of the same polymer as the non-foamed one layer exists. Such a bellows also has a reduced weight with the same stability, is radial softer and therefore less sensitive to impact and has improved diffusion behavior if suitable barrier layers are used.

The improved diffusion behavior is advantageous if, for example, there is grease in the bellows and the oil in the grease is lost through diffusion and with it its lubricating properties. A suitable barrier layer prevents diffusion and preserves the lubricating properties of the grease.

As already described above, the first layer can consist of a non-foamed material and the second layer can consist of a foamed material. In order to provide the best possible protection for the second layer made of the foamed material from undesirable influences, it can be provided that the second layer is sandwiched between the first layer and a third layer. The foamed second layer then no longer comes into contact with the inner and outer surroundings of the bellows and is protected in the best possible way.

The third layer and the first layer can be made of the same material.

The best way to recycle is a bellows in which all layers consist of the same material, the material of the first and third layers preferably being non-foamed, while the material of the second layer preferably be foamed.

With regard to a simple and process-reliable method for producing the bellows, it can be provided that the first layer and the third layer each have a substantially constant wall thickness. The advantage here is that all areas of a respective layer can be produced easily and free from production-related errors and the bellows is therefore good and has predictable performance characteristics over a long period of use.

It is also advantageous if the first layer and the third layer have essentially the same wall thicknesses. During the manufacturing process, these layers behave largely the same, for example with regard to hardening and/or shrinkage.

The wall thickness of the second layer is preferably greater than the wall thickness of the first and third layers if the functional layers, which are generally expensive, are on the outside.

The wall thickness of the second layer is preferably smaller than the outer ones if it has a high strength and a higher Young's modulus than the outer layers. It then has a strength-increasing character and affects flexibility as little as possible. The same applies to barrier layers that reduce permeability if their material has a higher modulus of elasticity.

For most applications, for example in the automotive sector, the layers have wall thicknesses of 0.3 mm to 3 mm.

If the walls are thinner, the durability of the bellows is limited during its intended use; if the walls are thicker, the bellows often no longer has the required resilience.

The use of a bellows with a multi-layer structure as an axle or steering boot of a motor vehicle is particularly advantageous. It is particularly advantageous because the multi-layer construction of the bellows means that layers with different properties can be obtained, so that the technical requirements can be met in the best possible way. The technical ones Requirements are low weight, good heat insulation, low friction, low noise, low oil permeability, increased service life.

The advantages mentioned can also be of advantage for other uses, for example for a bellows for a steering gear of a motor vehicle, a protective bellows for a spring strut of a motor vehicle or a stop bellows externally or internally of a spring strut of a motor vehicle.

The bellows can additionally have a substantially cylindrical area to increase stability.

The invention also relates to a method for producing a bellows with an at least two-layer structure, comprising at least one first layer and at least one second layer, all layers being produced simultaneously by coextrusion in a common coextrusion tool and brought together to form the bellows for production reasons and in connection with the already mentioned advantageously mentioned material compatibility are thereby inextricably linked. Coextrusion is essentially just as easy to perform as extrusion blow molding of a single-walled component. Molten polymer is pressed through nozzles via a screw conveyor, resulting in a tubular semi-finished product. This tubular semi-finished product is then inflated in a blow mold and thereby adapted to the inner contour of the blow mold.

Brief description of the drawing

An embodiment of a bellows according to the invention is based on the Figures 1 to 3 explained in more detail.

Figur 1

eine perspektivische Ansicht eines gebrauchsfertigen, dreischichtigen Balgs,

Figur 1a

den Balg aus Figur 1 mit einem herausgetrennten Ausschnitt, um den mehrschichtigen Aufbau besser zeigen zu können,

Figur 2

einen vergrößerten Schnitt durch den dreischichtigen Balg aus Figur 1,

Figur 3

einen weiter vergrößerten Ausschnitt aus dem Balg gemäß Figur 2.

These each show a schematic representation:

figure 1

a perspective view of a ready-to-use, three-layer bellows,

Figure 1a

out the bellows figure 1 with a cutout cut out to better show the multi-layered construction,

figure 2

an enlarged section through the three-layer bellows figure 1 ,

figure 3

a further enlarged section of the bellows according to figure 2 .

implementation of the invention

In the Figures 1 to 3 an embodiment of a bellows according to the invention is shown, which has a three-layer structure with a first 1, second 2 and third layer 3.

figure 1 shows a perspective view of the bellows. The bellows is used as an axle boot in a motor vehicle and is designed as a bellows.

In Figure 1a the bellows is off figure 1 shown with a 90° cut out. This shows the multi-layer structure of the bellows.

In figure 2 is a section through a fold of the bellows figure 1 shown. The bellows has a three-layer structure and includes the first 1, the second 2 and the third layer 3. All three layers 1, 2, 3 are production-related inseparably connected and consist of a matching TPE material.

Because the bellows is made of the same material, it can be recycled without any problems and sorted by type.

The first layer 1 and the third layer 3 are arranged on the opposite sides of the second layer 2, with the bellows being constructed in a sandwich-like manner. The middle second layer 2 consists of a foamed material, while the first layer 1 and the third layer 3 consist of a non-foamed material. As a result, the second layer 2 has a lower density than the two adjacent layers 1, 3.

In figure 3 the section "X" is off figure 2 shown enlarged.

In the exemplary embodiment shown, each layer 1, 2, 3 has an essentially constant wall thickness 4, 5, 6, with all layers 1, 2, 3 also having essentially the same wall thicknesses 4, 5, 6. Due to the essentially constant wall thicknesses of each layer and the fact that all layers have essentially the same wall thicknesses 4, 5, 6, the bellows can be produced simply and reliably by coextrusion.

In particular, the foamed second layer 2 is of particular advantage. Due to the comparatively low density, material is saved in relation to the two adjacent layers 1, 3, so that the bellows shown can be produced inexpensively and is light.

Claims (10)

1. Bellows having an at least two-layer construction, comprising at least a first layer (1) and at least a second layer (2), which are connected to one another in a non-releasable manner as a result of their production, wherein the layers (1, 2) have densities that differ from one another, characterized in that the first layer (1) and the second layer (2) consist of the same material, and in that the material of one of the layers (1, 2) is unfoamed and the material of one of the layers (2, 1) is foamed.
2. Bellows according to Claim 1, characterized in that the first layer (1) consists of an unfoamed material, in that the second layer (2) consists of a foamed material, and in that the second layer (2) is arranged between the first layer (1) and a third layer (3) in a sandwich-like manner.
3. Bellows according to Claim 2, characterized in that the third layer (3) is formed in a materially uniform manner with the first layer (1).
4. Bellows according to one of Claims 2 or 3, characterized in that the first layer (1) and the third layer (3) each have a substantially constant wall thickness (4, 6).
5. Bellows according to one of Claims 2 to 4, characterized in that the first layer (1) and the third layer (3) have substantially identical wall thicknesses (4, 6) .
6. Bellows according to one of Claims 2 to 5, characterized in that the wall thickness (5) of the second layer (2) is greater than the wall thicknesses (4, 6) of the first layer (1) and of the third layer (3).
7. Bellows according to one of Claims 4 to 6, characterized in that the wall thicknesses (4, 5, 6) are each 0.3 mm to 3 mm.
8. Bellows according to one of Claims 1 to 7, characterized in that the first layer (1) and the second layer (2) consist of a TPE material.
9. Use of a bellows according to one of Claims 1 to 8 as an axle boot or steering rack boot of a motor vehicle.
10. Method for producing a bellows according to one of Claims 1 to 8 having an at least two-layer construction, comprising at least a first layer (1) and at least a second layer (2), characterized in that all the layers (1, 2, 3) are produced at the same time in a common coextrusion tool by coextrusion and are joined together to form the bellows as a result of their production and are thereby connected to one another in a non-releasable manner.

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